1. Field of the Invention
The present invention relates to a transfer member such as an intermediate transfer body used by an electrostatic copying system image forming apparatus such as a copying machine or printer.
2. Description of the Related Art
In an electrostatic copying system image forming apparatus, an image bearing body comprising a photoconductive photosensitive material is uniformly electrified, an electrostatic latent image is formed with a laser beam obtained by modulating image signals, and a visible toner image is obtained by developing the electrostatic latent image with an electrified toner.
A so-called intermediate transfer system image forming apparatus is one of such image forming apparatus, wherein a desired reproduction image is obtained by electrostatic transferring the toner image via an intermediate transfer body. For example, Japanese Patent Application Laid-Open (JP-A) No. 62-206567 discloses such an image forming apparatus.
Examples of the material of the intermediate transfer body used in the image forming apparatus employing the intermediate transfer process using the intermediate transfer body include electroconductive endless belts of thermoplastic resins such as polycarbonate resins disclosed in JP-A No. 06-095521, PVDF (polyvinylidene fluoride) resins disclosed in JP-A Nos. 5-200904 and 6-228335, and polyalkylene phthalate resins disclosed in JP-A No. 6-149081; and polyimide resins and polyamide imide resins disclosed in Japanese Patent No. 2560727.
Aromatic polyimide resins are preferably used for the intermediate transfer body (transfer member) since such resins have high mechanical strength. The resistivity of the transfer member should be restricted to a prescribed range, and it is well known that the carbon black is blended with the resin for controlling the resistivity. However, irregular transfer or transferred image distortion may occur in this method unless carbon black is extremely finely dispersed in the resin. Since the aromatic polyimide resin are thermally stable and insoluble in solvents, to adjust the resistivity, carbon black should be dispersed into a poly(amic acid) as a precursor, or a resin member should be formed by polymerization after dispersing carbon black in a monomer solution to obtain the poly(amic acid) containing a resistance controlling agent, followed by removal of solvents and conversion into an imide after forming a film from either solution as described above.
For example, JP-A No. 2001-342344 discloses use of a dispersing machine using a media, wherein acidic carbon black, having a DBP absorption of 40 cm3 or more and 90 cm3 or less and volatile component of 2.5 wt % by weight or more per 100 m2/g of specific surface area, is finely dispersed in a poly(amic acid) solution as a few material of polyimide. However, this method is not satisfactory for maintaining stable resistivity. Moreover, when the dispersing machine using the media is used, the production cost becomes high when an expensive resin material such as a polyimide resin is used because the amount of loss of the material is as high as 20% in the medium and vessel. In addition, various drawbacks are encountered such as defects being generated due to contamination from the media and vessel, dispersing ability changing during use due to a reduced media diameter, and the method being unusable in a high viscosity system since high speed collision of the media is necessary.
On the other hand, JP-A No. 2000-355432 discloses forming polyimide from poly(amic acid) obtained by adding an acid anhydride and a diamine to a solvent in which resistivity control agent was dispersed. However, since various functional groups on the surface of carbon black are inconvenient for the polymerization reaction of poly(amic acid), the carbon black should be deactivated in advance.
JP-A No. 2001-34074 discloses an example in which carbon black is mixed with dimethylacetamide to a proportion of 15% by weight, and is dispersed by passing through a dual collision dispersing machine having grooves with a width of 0.1 mm and a depth of 0.1 mm at a pressure of 10 kgf/cm2 (about 1 MPa). However, it is thought that passing a mixture through the dual collision dispersing machine at the pressure as described above would be difficult.
JP-A No. 2001-106797 discloses a pipe-shaped polyimide containing 12% by weight (13.6 parts by weight) of a conductive material as the intermediate transfer body for obtaining a high quality transfer image with good reproducibility. However, in our testing, transfer images having sufficient image quality could not be obtained with such pipe-shaped polyimide.